1. Field of the Invention
The present invention relates to an optical switch and an optical switch device.
2. Description of the Related Art
Various optical devices are conventionally used in an optical communication field, etc. For example, there is an optical device constructed so as to have plural optical fibers and mirrors as an optical switch device for switching and interrupting the optical path of an optical fiber transmission line.
As shown in FIGS. 11 and 12, the optical switch device is constructed such that plural optical fibers 22a to 22d are aligned in parallel with each other on a substrate 21, and a movable reflection member 23 constructed by combining two reflection faces (mirrors) 23a, 23b is arranged in front of these optical fibers so as to be vertically moved by an unillustrated-cantilever (e.g., see patent literature 1). In this construction, a magnetic material is arranged in the cantilever and an electromagnet is arranged below the substrate 21 although this arrangement is not illustrated. The cantilever is vertically moved by operating the electromagnet so that the movable reflection member 23 can be switched to an advancing state into the front of the tips of the optical fibers 22b, 22c and a state retreated from this front. In the advancing state of the movable reflection member 23 into the front of the tips of the optical fibers 22b, 22c, reflection faces 23a, 23b are located within the optical paths of beams from the optical fibers 22a, 22c. Therefore, an optical path from the optical fiber 22a to the optical fiber 22b and an optical path from the optical fiber 22c to the optical fiber 22d are formed in cooperation with fixed reflection faces 24a, 24b. In contrast to this, in the state of the movable reflection member 23 retracted from the front of the tips of the optical fibers 22b, 22c, no reflection faces 23a, 23b are located within the optical paths of the optical fibers 22a, 22c, and an optical path from the optical fiber 22a to the optical fiber 22d and an optical path from the optical fiber 22c to the optical fiber 22b are formed by using the deeply fixed reflection faces 24a, 24b. The optical switch for switching the optical paths of the optical fibers is constructed in this way.
[Patent Literature 1]
JP-A-2000-137177 (paragraphs [0017] to [0027] and FIG. 1).
In the above conventional construction, the optical fibers 22a to 22d are arranged in parallel with each other at an equal interval (pitch A). This arrangement has the advantage that the optical fibers 22a to 22d can be easily held and constructed. However, in such a construction that the movable reflection plates 23a, 23b and the fixed reflection plates 24a, 24b are arranged in front of the optical fibers 22a to 22d arranged in parallel with each other at the equal interval, there is a possibility that the difference in optical path length before and after the switching of the optical paths is increased. Namely, as shown in FIG. 12, the optical path from the optical fiber 22a to the optical fiber 22b and the optical path from the optical fiber 22c to the optical fiber 22d in the inserting case of the reflection plates 23a, 23b differ in length from the optical path from the optical fiber 22a to the optical fiber 22d and the optical path from the optical fiber 22c to the optical fiber 22b in the uninserting case of the reflecting plates 23a, 23b. Concretely, the optical path length between end face from the optical fiber 22a to the optical fiber 22b is E+A+E=A+2E. The optical path length between end portions from the optical fiber 22c to the optical fiber. 22d is also E+A+E=A+2E. However, the optical path length between end portions from the optical fiber 22a to the optical fiber 22d is E+A+A+A+E=3A+2E. The optical path length between end portions from the optical fiber 22c to the optical fiber 22b is E+D+A+D+E=A+2D+2E. Thus, a large difference in optical path length is caused before and after the switching using the optical switch.
In an optical device such as an optical switch, a fiber collimator of a relatively small diameter having a graded index optical fiber is used in many cases. A beam emitted from the fiber collimator is once converged and is then again widened and advanced. As one example, as shown by the situation of the advance of the emitted light in Table 1 and FIGS. 13 and 14, the beam diameter is changed in accordance with the distance from the end face of the optical fiber.
TABLE 1Distance (μm)Beam radius (μm)−25048.9−20042.4−15036−10029.5−5023.1016.65027.210037.815048.420059.125069.8
Therefore, when this fiber collimator is assembled into the optical device, a pair of optically connected fiber collimators can be held with high coupling efficiency by arranging this pair of fiber collimators in a position relation for optimizing the distance between their end portions on the basis of the converging and enlarging states of light. Namely, when the same fiber collimator is used on the emitting side and the incident side, it is preferable to set the fiber collimator so as to have a focal point in a halfway spot.
The arranging position of the fiber collimator within the optical device is determined in this way. However, in the case of the construction as shown in FIG. 12, for example, when the optical fiber is arranged so as to optimize the optical path length (A+2E) of the optical path before the switching, there is a high possibility that light is incident to another optical fiber while the light state is inappropriate as it is in an excessively large state of the beam diameter, at the optical path length (3A+2E, A+2D+2E) of the optical path after the switching. In this case, insertion loss is increased.
Here, the relation of the distance between the pair of optical fibers and the coupling efficiency will be explained. FIGS. 15A to 15C show a case in which the position for focusing the beam from one (left-hand side) optical fiber (the position for setting the beam radius to 16.6 μm as a minimum radius) is set to 0 μm, and the distance is displayed, and the position of the tip end face of the other (right-hand side) optical fiber is changed. Here, when it is considered whether the focal point positions from both the optical fibers are conformed to each other, the coupling efficiency is calculated, by the following Marcus formula.η=[(2W1W2)/(W12+W22)]2  [Formula 1]                η: coupling efficiency        W1: beam radius from one optical fiber        W2: beam radius from the other optical fiber        
The coupling efficiency is calculated on the basis of this Marcus formula and loss is further calculated. The calculated results are shown in Table 2 and FIG. 16. Here, as one example, the beam of about 50 μm in radius is emitted and the focal point is formed at a distance of 250 μm from the emitting end. Namely, the fiber collimator is used so as to set the beam diameter to a BW (Beam Waist) point as a minimum beam radius and having a 3.5 distribution constant and a 125 μm diameter (100 μm in core diameter).
TABLE 2Distance (μm)Coupling efficiency (%)Loss (dB)−25037.14.31−20046.13.36−15057.82.38−10073.11.36−5089.80.47010005079.11.0210054.22.6615037.74.2420027.15.6725020.36.93
As can be seen from these results, the coupling efficiency is best and the loss is reduced when both the optical fibers are arranged such that the distance between their tip portions is equal to 500 μm so as to conform the focal points (BW points) of both the optical fibers as shown in FIG. 15A. However, the coupling efficiency is greatly reduced and the loss is increased even when the distance between both the optical fibers is slightly receded. For example, as shown in FIG. 15B, when the optical fiber on the emitting side (left-hand side) is fixed as it is and the optical fiber on the incident side (right-hand side) is separated by 100 μm, the coupling efficiency is reduced until 54.2%. As shown in FIG. 15C, the coupling efficiency is also reduced to 73.1% when the optical fiber on one side (left-hand side) is fixed as it is and the optical fiber on the other side (right-hand side) approaches by 100 μm. To restrain the loss to 0.5 dB or less, it is necessary to arrange both the optical fibers so as to optically couple the optical fibers in the range from +25 μm to −50 μm.
Thus, the coupling efficiency is greatly reduced and the loss is increased even when the distance between the optically connected optical fibers is changed only by several ten μm. Accordingly, when the optical switch device is constructed so as to change the optical path length before and after the switching of the optical switch as mentioned above, there is a high possibility that, even when light is preferably propagated with high coupling efficiency in one of the optical path before the switching and the optical path after the switching, the coupling efficiency is low in the other and the propagation of light becomes bad.
Further, in the conventional construction shown in FIGS. 11 and 12, the reflection plate 24a on the fixing side is located in front of the optical fibers 22a and 22b and reflects the beam. The reflection plate 24b is located in front of the optical fibers 22c and 22d and reflects the beam. Therefore, it is necessary to set the reflection plates 24a, 24b to have a relatively large area. Further, the movable reflection plates 23a, 23b are integrated in a unit as the movable reflection member 23 so that the reflection plates 23a, 23b are large-sized. Thus, since the arranging area of the reflection plates (mirrors) is increased, the distance from the emission from the optical fibers 22a, 22c to the arrival at the reflection plates is necessarily lengthened so that the optical path lengths reaching the optical fibers 22b, 22d are lengthened. When the optical path length is lengthened, the optical path length has a large influence even when the relative shifts of the positions and the angles of the optical fibers 22a to 22d and the reflection plates 23a, 23b, 24a, 24b are small, thereby increasing the light loss. This means that a very precise and complicated assembly work is required. Further, since the movable reflection plate 23 is large-sized, it is necessary to set the cantilever as its driving means to be large-sized and increase the output of the electromagnet. Further, there is a fear that resonance frequency is reduced and switching speed must be reduced, which is not suitable for high speed optical communication. Further, since the entire optical switch is large-sized as a result, the number of optical switches able to be manufactured from one wafer is reduced. Therefore, a problem exists in that manufacture cost is raised.
Further, the use of the conventional optical switch is limited to the switching of the optical path. However, in the optical communication, a part having a function for attenuating the light amount is required in addition to the optical path switching functional part. When these functional parts of the different actions are used, the shapes of the functional parts are different from each other so that no functional parts can be aligned with each other and no arranging area thereof can be reduced. Further, problems exist in that the constructions of the functional parts are different from each other so that the used parts and their manufacturing processes are different from each other and no cost can be restrained.